Well, yes and no.
Can you just stop paying the $250/month and pocket the money? No. That would be a material breach of the contract on your part -- not something you want to do.
However, you CAN see your lawyer about this problem. It is possible that you have a cause of action against X for breach if the service is part of the contract for which you are paying. Winning this could at least get you your money back.
Is the inadvertent lack of signature on the contract paperwork a way out of the contract? Probably not at this point; you're halfway through the contract and the contract terms have been performed thus far, at least by you.
Good luck with it.
I disagree with Ms. Delain. If you pay them, you have no bargaining room. I would withhold payment and send a letter to the company requesting that they do something to alleviate your concerns. Maybe they could provide an additional three months at no additional charge, or reduce your monthly rate to $200. Do they have an enforceable contract? Possibly, but you will get nothing done without trying. Companies are in the business of making money and many companies would rather work something out than sue you for the money. If they pay hardball you can always issue payment of $1,500 and end the matter.